21 



CHAPTEE IV. 



ON THE EXTERNAL ANATOMY OF THE COLEOPTEEA. 



IT will be necessary to enter somewhat fully into the 

 position and names of the various parts of the external 

 anatomy of Beetles, as they are constantly referred to 

 in all works, either of description or classification ; and 

 the common Water-beetle (Dytiscus marginalis] , before 

 alluded to, will act very well as a type, owing to its large 

 size, and the well-defined outline of its component 

 parts : it cannot, however, be taken as a perfect stan- 

 dard, as its paraglossse and metathoracic epimera are 

 obsolete, and its hinder coxae are enormously developed. 

 The body is usually considered to be divided into three 

 segments, with their respective appendages : viz. the 

 head, with the eyes, antennae, and mouth- appar atus ; 

 the thorax, with the elytra, wings and legs; and the 

 abdomen, with the organs of generation. These seg- 

 ments are in reality composed of numerous separate 

 parts, which we will now proceed to mention ; there is. 

 however, no occasion to enter very fully into the details 

 of external structure, for which the student can refer to 

 the works of Burmeister, Kirby and Spence, etc, : but 

 the principal parts of the body, with the names by which 

 they are now usually known, must be enumerated, 



